Enable text based alternatives for graph display and drawing entry

Click here to erase all data entry on this page

Purpose

        To work with electrical energy storage using capacitors and see how they charge and discharge.

Connections to What You Already Know About in Life

        Many machines that we use today need bursts of electrical energy to work properly. For example, think of the windshield wipers used in a car. They store energy in a capacitor and then release that energy through the mechanical swing of the wiper. Or, think of the computer running this physics program—it has capacitors that store charge to provide some filtering of the electronic signals in the computer.

Vocabulary

Breadboard, capacitance, function generator, oscilloscope

Background

         Capacitors take time to charge and discharge and so they don’t instantly lose all of their charge. Capacitance is related to the amount of voltage potential in a capacitor. You will look at different capacitors and the maximum voltages they can have. Because capacitors charge very quickly, we use the resistor to impede, or block, the current and it will allow you to see the charging and discharging at a slower rate.

Pre-Lab Question

  1. What will happen to the time it takes to charge and the maximum voltage in a capacitor if you increase the capacitance of the capacitor?

Procedure

  1. Start Virtual Physics and select Capacitors from the list of assignments. The lab will open in the Circuits laboratory.
  2. The laboratory will be set up with a resistor (initially 10,000 W) and a capacitor connected on the breadboard. A Function Generator is also connected to the breadboard. The Function Generator will be set to 10 V DC and it will be on.
  3. The oscilloscope will be connected across the capacitor. The multimeter is also connected, which will display the voltage across the capacitor.
  4. Observe what happens to the voltage across the capacitor and record your observations in the data table. You may want to use the Acceleration button on the oscilloscope to increase the speed of the charging but remember to change it back to 1 when you are done charging it. This may take a few minutes.
  5. You should also change the resistor on the breadboard to smaller and larger values (1,000 W and 100,000 W) and observe what happens. You can change component values on the circuit diagram by clicking on the component and typing in the new value.
  6. Once the capacitor is fully charged (the voltage does not change any more), clear the breadboard by clicking on the Reset Lab button at the bottom of the table, click on the clipboard on the right, and click on Discharging Capacitor (#7) preset experiment. You should see the same experiment except this time the capacitor is discharging. Record your observations of how the voltage changes over time for the discharging capacitor.
  7. Repeat step 6, except this time when the preset experiment starts, change the resistor to 1,000 Ω.
Capacitance (mF) Resistance (Ω) State Observation Maximum Voltage (V)
100 10000 Charging
100 Charging
100 Charging
100 100 Discharging
100 1000 Discharging

Questions

  1. What happened to the voltage across the capacitor when it was connected to the voltage source?

  1. How did the time to charge and discharge the capacitor change when you changed the resistance of the resistor?

  1. Using the information gathered, can you explain why keyboards would use capacitors for each key button? Think about how you got the capacitor to charge and discharge.

  1. Why must you be careful when taking apart electronics?